1. Field of the Invention
This invention relates to a refrigerating cycle apparatus equipped with an economizer, and, more particularly, it is concerned with increase in the air-conditioning capability and the coefficient of performance of such refrigerating cycle apparatus.
2. Discussion of Background
FIG. 7 of the accompanying drawing is a Mollier's diagram showing a refrigerating cycle, wherein the abscissa denotes an enthalpy h [kcal/kg], and the ordinate represents a pressure p [MPa]. In this graphical representation, a reference letter Pc denotes a condensing pressure [MPa] in the refrigerating cycle, and a reference letter Pe represents an evaporating pressure [MPa] in the refrigerating cycle.
Further, in this graphical representation, a region at the left side of a curve belongs to a liquid phase of the refrigerant, the center part enclosed by the curve denotes a two-phase section, and a region at the right side thereof represents a gas phase. In the drawing, the enthalpy of the refrigerant corresponding to reference numerals 51 to 54 are designated by h.sub.51 to h.sub.54 respectively. The refrigerant with its enthalpy of h.sub.51, when it is compressed by a compressor, turns into a state, in which it has the enthalpy of h.sub.52. This refrigerant is cooled under a substantially constant pressure in a condenser within the refrigerating cycle apparatus, and then liquefied to be a liquid refrigerant having its enthalpy of h.sub.53. By means of a throttle provided in the refrigerating cycle apparatus, the liquid refrigerating medium having its enthalpy of h.sub.53 performs an isenthalpic expansion, whereby the pressure lowers to an evaporating pressure Pe to assume a two-phase state. The enthalpy h.sub.54 at this time has the identical value with the enthalpy h.sub.53. The refrigerant in two phases is heated by the evaporator provided in the refrigerating cycle apparatus, and is evaporated. Upon its heating, the liquid refrigerant is again turned into vapor having its enthalpy of h.sub.51, and is compressed by the compressor. The above is the fundamental principle of the ordinary refrigerating cycle which has been in wide use. By the way, the term "refrigerating cycle apparatus" is used as a general term for a refrigerant cycle apparatus, heat-pump device, vapor-compressing type refrigerating cycle apparatus, and so forth.
Now, in a refrigerator to be used at a high compression ratio, the compression and refrigeration cycle comprises two or more stages, and an economizer is provided at each stage to separate the refrigerant into the gas phase and the liquid phase so as to improve the coefficient of performance in the refrigerating cycle.
FIG. 8 is a conceptual diagram showing a two-stage compression type refrigerating cycle apparatus provided with the economizer. In the drawing, a reference numeral 5 designates an evaporator, a numeral 1 refers to a compressor at a low compression stage side, a numeral 2 refers to a compressor at a high compression stage side, a reference numeral 3 represents a condenser, a reference numeral 6 denotes a first throttle, a numeral 4 refers to an economizer, and a numeral 7 indicates a second throttle, all these component elements being connected in the order as mentioned. The first throttle 6 and the second throttle 7 comprise, for example, expansion valves, capillaries, and so forth. A reference numeral 8 designates a piping for the economizer, which connects the gas phase portion of the economizer 4 and the inlet side of the high compression stage side compressor 2 (i.e., an intermediate pressure region between both low stage side compressor 1 and high stage side compressor 2). In the drawing, reference numerals 51 through 59 represents various states of the refrigerant at its every position as designated. Also, an arrow mark indicates the flowing direction of the refrigerant.
FIG. 9 is a Mollier's diagram of the refrigerating cycle shown in FIG. 8. When this refrigerating cycle is used in the cooling mode, for example, the refrigerant is separated into liquid refrigerant having the enthalpy of h.sub.58 in its pressure state of Pm within the economizer 4, i.e., liquid phase refrigerant (in the saturated condition) and gas phase refrigerant having the enthalpy of h.sub.57, i.e., gas phase refrigerant (in the saturated condition), hence the effect of refrigeration in this cycle will be (h.sub.51 -h.sub.59). Here, in the case of no economizer being used, the effect of refrigeration will be equivalent to (h.sub.51 -h.sub.56), which has the following relationship as is apparently seen from FIG. 8: (h.sub.51 -h.sub.59)&gt;(h.sub.51 -h.sub.56). As the consequence of this, the cooling capability would increase by the use of the economizer. Moreover, since the input of the refrigerant into the compressor does not increase so much, the refrigerating cycle also increases its coefficient of performance as has been well known.
In the next place, when the cycle in FIG. 9 is used in the heating mode, if an economizer is employed, a flowing quantity g [kg/h] of the gas which has been separated at the intermediate pressure Pm passes through the condenser in addition to a flowing quantity G [kg/h] of the refrigerant which the compressor is able to circulate in the cycle, on account of which the warming capability would increase for the quantity g. In this case, too, since the input of the refrigerant into the compressor does not increase so much, the cycle would augments its coefficient of performance, as has been well known.
As so far been described, both cooling and warming capabilities increase with use of the economizer.
Now, considering the Mollier's diagram in FIG. 9, the following equation is established from the energy relationship on the part of the economizer 4: EQU Gh.sub.58 +gh.sub.57 =(G+g)h.sub.56.
From the above equation, the following relational expression may be derived ##EQU1## From the above equations (i.sub.1) and (i.sub.2), it will be seen that G and g cannot be independent of each other, but each of them varies in association.
The quantity of gas g [kg/h] flowing from the economizer 4 is usually governed by the diameter of the piping for the economizer. Also, from the Mollier's diagram, it can be explained that the increased quantity (h.sub.56 -h.sub.58 (=h.sub.56 -h.sub.59)) for the refrigerating effect in FIG. 9 becomes large with a lower value of the pressure Pm in the economizer.
FIG. 10 indicates a relationship between the pressure Pm in the economizer and the increased quantity for the refrigerating effect. As is apparent from this graphical representation, the increased quantity (h.sub.56 -h.sub.58) for the refrigerating effect can be primarily determined with respect to an arbitrary pressure Pm in the economizer.
The conventional refrigerating cycle provided with the economizer is constructed as mentioned above. However, it has a problem such that, when its operating conditions are set, its operating efficiency on the Mollier's diagram, i.e., increase in the cooling or warming capability, and increase in its coefficient of performance are substantially established, so that it becomes difficult to realize further improvement in the operating efficiency of the refrigerating cycle.
Moreover, the same problem is also present in a refrigerating cycle apparatus such as, for example, a rotary compressor, etc., wherein the refrigerant is supplied to the compressor from a suction muffler to a suction pipe.